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Principles Of Pharmacology > Week 4 > Flashcards

Week 4 Flashcards

1
Q

What is the collective name for metabolism and excretion of drugs?

A

Elimination

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2
Q

What is the main site of drug metabolism in the body?

A

Liver

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3
Q

Name some areas of the body that have metabolic activity.

A 
Liver
Gastrointestinal tract
Skin
Lungs
Kidneys
Neurones
Blood
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4
Q

What are the 2 main effects of metabolism on drugs?

A

Increased water solubility

Reduced pharmacological activity

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5
Q

What is the purpose of increasing water solubilityof a drug?

A

Enables urinary excretion

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6
Q

What must happen to a drug for it to be excreted from the body?

A

Its lipid solubility must decrease and its water solubility must increase

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7
Q

Why will a drug which is lipid soluble not be excreted?

A

It will move by simple diffusion from the renal tubule of the nephron of the kidney to the peritubular capillaries surrounding the kidney and reach the heart via the circulation. It will continue to re-enter the circulation.

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8
Q

What is the main property of a drug required for it to be absorbed and distributed around the body?

A

Must be lipid soluble

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9
Q

What is the purpose of Phase 1 metabolism?

A

Functionalizing.

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10
Q

How is a drug caused to become active in phase 1 metabolism?

A

A chemically reactive, polar molecule is added to the drug, usually via an oxidation reaction

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11
Q

What type of reaction is used to make drugs chemically active in phase 1 metabolism?

A

Usually oxidation reaction

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12
Q

What enzymes are used in phase 1 of drug metabolism?

A

CYP450

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13
Q

What are the overall effects of phase 1 of drug metabolism?

A

Used to reduce toxicity and pharmacological effects of a drug

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14
Q

Where does phase 1 of drug metabolism occur?

A

Liver

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15
Q

What is the overall purpose of phase 2 of drug metabolism?

A

Forming a water soluble drug from a chemically active drug.

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16
Q

Where does phase 2 of drug metabolism occur?

A

In the liver

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17
Q

What is the overall process which occurs during phase 2 of drug metabolism?

A

Conjugation

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18
Q

What chemically happens during phase 2 of drug metabolism?

A

A polar reactive molecule is attached to the drug to result in a water soluble product

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19
Q

What are xenobiotic compounds?

A

Compounds which are foreign to the body but can be found in the biosphere.

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20
Q

What type of enzymes have the ability to break down Xenobiotics?

A

CYP450

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21
Q

How can Xenobiotics enter the body?

A

Frequently enter via the food.

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22
Q

What are CYP450 enzymes?

A

A large number of relative oxidative enzymes which are responsible for the metabolism of thousands of endogenous and exogenous drugs

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23
Q

Where are P450 enzymes mainly found?

A

In the membranes of the small endoplasmic reituclum and mitochondria of hepatocytes

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24
Q

What are hepatocytes?

A

A cell of the main parenchymal tissue of the liver.

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25
Q

How do P450 enzymes oxidise drugs?

A

They add an oxygen atom to form a hydroxyl group on the drug which can then be reacted in phase 2 of metabolism.

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26
Q

What type of enzymes metabolise phase 2 of drug metabolism?

A

Specific transferase enzymes

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27
Q

Where are the transferase enzymes used for phase 2 of drug metabolism found?

A

Bound to the endoplasmic reticulum or free in the cytoplasm of hepatocytes

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28
Q

What is the overall objective of phase 2 of drug metabolism?

A

To reduce the toxicity and pharmaceutical effects of a drug.

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29
Q

What are endogenous molecules?

A

Molecules which originate inside the body

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30
Q

What are exogenous molecules

A

Molecules which originate outside the body

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31
Q

Outline the negative effects that can occur due to metabolism of codeine.

A

A small proportion of codeine can be metabolised into morphine which is more pharmaceutically active than codeine

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32
Q

What is an analgesic?

A

A drug used to relieve pain

33
Q

What is meant by the term ‘potency’?

A

The ability of a drug to cause a pharmaceutical effect.

34
Q

Which isomer of warfarin is the most potent?

A

S isomer

35
Q

What are the 2 isomers of warfarin?

A

S and R

36
Q

What are the effects of having too much CYP2D6 on metabolism of codeine?

A

Too much - rapid metabolism of codeine to morphine. Can reach toxic levels of morphine in the body.
Too little - insufficient metabolism of codeine to morphine. Anagelsic effects or morphine not felt.

37
Q

What enzyme is used to metabolise codeine into morphine?

A

CYP2D6

38
Q

In normal therapeutic doses, what is Paracetamol conjugated into?

A

Glucoronide and Sulphate

39
Q

What is the toxic product that can be formed in phase 1 metabolism of paracetamol?

A

NAPQI

40
Q

In what phase of metabolism can paracetamol be metabolised into a toxic intermediate?

A

Phase 1

41
Q

What reaction type causes paracetamol to form a toxic NAPQI intermediate during metabolism?

A

Oxidation using P450 enzymes

42
Q

Why are the toxic effects of metabolism of paracetamol into NAPQI often not felt by the body?

A

NAPQI quickly reacts with Glutathione and is further converted to non-toxic conjugates which are excreted via the kidney.

43
Q

What happens if Glutathione levels are low in the body and alot of paracetamol has been converted to NAPQI in phase 1 of metabolism?

A

The toxic NAPQI will build up in the body and cause severe damage to the kidney which can lead to liver failure.

44
Q

What happens when someone overdoses on paracetamol?

A

Glutathione levels are rapidly depleted and so toxic levels of NAPQI metabolite cause hepatic and renal damage which can cause death by liver failure.

45
Q

What antidote is used for paracetamol overdose?

A

N-acetylene cysteine

46
Q

How does N-acetylene cysteine acts as an antidote for paracetamol overdose?

A

Absorbs NAPQI and therefore reduces its toxic effects in the body

47
Q

What is used to determine when an individual should be given an antidote to a drug?

A

A treatment nomogram

48
Q

What does a treatment nomogram show?

A

The concentration of a drug in the body against time and at what concenetration it will move out of the therapeutic range.

49
Q

Outline the routes of drug excretion.

A 
Urine
Bile
Faeces
Sweat
Breath
Saliva
Milk
Hair
50
Q

What type of drugs are excreted via urine?

A

Drugs with a low molecular weight

51
Q

What type of drugs are excreted via bile?

A

Larger, high molecular weight substances which are often conjugated.

52
Q

What type of drugs are excreted via faeces?

A

Compounds excreted through bile and materials which have not been absorbed by the gut.

53
Q

What type of drugs are excreted via sweat?

A

Water soluble drug products

54
Q

What is ‘the gut’?

A

The full digestive tract

55
Q

What type of drugs are excreted via breath?

A

Volatile substances

56
Q

What type of drugs are excreted via saliva?

A

Low molecular weight compounds

57
Q

What type of drugs are excreted via lactation (milk)?

A

Lipid and water soluble products

58
Q

What are the negatives of drug elimination via the hair?

A

Very slow

59
Q

What is rate of elimination of a drug proportional to in a first orderreaction?

A

Concentration of drug in the body

60
Q

How does an increased concentration of drug in the body affect rate of elimination in a first order reaction?

A

Increased concentration= increased rate

61
Q

Outline the shape of a first order kinetics graph of drug concentration against time.

A

(

62
Q

What is a first order reaction in terms of drug elimination?

A

Rate of elimination is directly proportional to concentration of drug.

63
Q

Define ‘half life’ of a drug.

A

The time taken for the concentration of a drug in the plasma to decrease by half its initial concentration

64
Q

What is the calculation for determining half life of a drug?

A

(0.693 x volume of distribution)/ clearance

65
Q

What is ‘clearance’ of drug?

A

The volume of blood cleared of drug per unit of time

66
Q

What is a zero order reaction in terms of drug elimination?

A

Elimination of drug is independent of the concentration of drug in the body.

67
Q

Give examples of drugs which have a zero order reaction.

A

Alcohol, phenytoin, warfarin, aspirin

68
Q

What is the approximate elimination rate of alcohol from the body?

A

10ml per hour

69
Q

What causes zero order elimination of drugs from the body?

A

When all enzymes become saturated, zero order reactions occur.

70
Q

Draw the shape of a zero order reaction graph.

A

\

71
Q

What enzyme enables to conversion of codeine to morphine?

A

CYP2D6

72
Q

Where does drug metabolism mainly occur?

A

Liver

73
Q

Which enzymes are involved with Phase 1 metabolism and where are they located?

A

CYP450 - found in the hepatocytes of the smooth endoplasmic reticulum and mitochondria.

74
Q

What factors can affect metabolism?

A 
Age
Muscle mass
Gende
Genetics
Body size
Physical activity
Hormonal balance
Environmental factors
Diet
Drugs
75
Q

Which enzyme converts codeine to morphine?

A

CYP2D6

76
Q

How is paracetamol metabolised at normal doses?

A

It is conjugated by glucoronide or sulphate via phase 2 metabolism.

77
Q

What % of drugs are first order?

A

95%

78
Q

Name some drugs which are zero order.

A

Alcohol, ethanol, phenytoin, salicylates, cisplatin, fluoxetine, omeprazole

Principles Of Pharmacology (11 decks)

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